This is Part 13 of our weekly North Carolina Criminal Defense video blog: “How Common are Breathalyzer False Positives?“
I think the manufacturers of the instruments that you blow into would say that they are truly accurate. They certainly have an interest because the instruments themselves are expensive. They have an interest in selling them as completely accurate.
Breath testing is, to some extent, based on a number of chemical, scientific theories that clearly don’t always apply to the human body. The breath testing instrument relies on Henry’s Law. Henry’s Law only applies when the system is closed, and equating Henry’s Law to the human body doesn’t really apply. There are things about breath testing equipment that can lead to inaccuracies.